Sometimes you can read on winemaking forums the horror stories about bottles of wine that started refermenting and caused a real mess or even an explosion. Well there are two things needed for a refermentation: residual sugar and living yeastcels that can reform a yeast colony.

And sometimes a spontaneous fermentation starts in a must or juice. Well not really spontaneous. Air-borne yeast cells or a contaminated spoon or other winemaking aid can start a fermentation.

Now on winemaking forums for years the story goes that just one single yeast cell is needed to start a complete new colony and can have your wine refermenting. That is what I would like to research.

First I need to confess that I made things easy for the yeast. I made a juice with the best conditions for fermentation. I took 1 liter apple juice and added sugar till there was 200 gram sugar in the juice. I also added nutrients.

However to make sure that it was MY yeast that would start things and no bacteria or yeast present in the bottle or juice I boiled the juice and sterilised the bottle with sulphite. Then I waited till the bottle had cooled down and the juice was lukewarm.

Next I took my yeast and carefully took out 1 grain. Well what we can see it the bare eye as 1 grain are actually already a few grains. However as this is my kitchentavble laboratory and not a real laboratory I can not split it further anymore and therefore it has to do.

Now the theory tell that each yeast cell splits each half our. Maning that if you start with 1 yeast cel in half an hour there will be 2 and another half hour later there will be 4. Afther 1.5 hour there will be 8, afther 2 hour 16 etc etc etc. This process continues untill a certain saturation point has been reached. At that time fermentation continues but yeast cells will not reproduce anymore. Mind you it means that there are billions of yeast cells present in each cl at that time.

Day 1

So on friday morning at 9 o'clock I dropped my grain of yeast in the must and the waiting started.

At 10 o'clock nothing happened. Well I actually did not expect at that time to see any activity.

After 2 hours still no activity. Again not surprising. According to the calculations there would just be 8 cells in the total must. And 8 cells in a liter will not make a lot noise. Off course I was curious and checked the must every hour.

In the evening at 10 o'clock there was still no activity visible and later on I went to bed.

Day 2

The next morning there was still no activity. Aagin each hour I checked the must but no sign of fermentation during the whole day. Even at 10 o çlock in the evening there was no sign of any activity. I started to worry a bit. Was the story a hoax ??? Was it just a fairy tale that one yeast cell could get a whole barrel going.

At this point 36 hour had passed since I dropped that 1 cel in the must. And 36 hour is 72 half hour. So the must should contain the incredible amount of 2^72 yeastcells (4722366482869650000000).......

Day 3

It was sunday. At 12 o'clock I saw that the must was cloudy. An obvious sign of activity.

At 3 o'clock some foam started to form.

In the evening at 6 o'clock more spots of foam where visisble.

And at 8 o'clock little bubbles where visible.

Day 4

Monday morning at 7 o'clock a layer of foam was clearly visible. The experiment succeeded !!! Fermentation was on its way.

The next days.

Every day there were visible (and audible) signs of fermentation just like you would see in any must. Afther a few days however fermentation was less vigorous and started decreasing.

The first few days however fermentation was vigorous and I could have used this must as a yeast starter for a new wine.

Day 11

On day 11 the juice was again perfectly clear.

The must had ceased fermentation and the wine should be ready. Only one way to make sure: measuring.

And indeed the SG was below 1000. The must had finished fermenting, the wine was ready.

Concluding.

I can never be sure that it was my one yeast cell that I dropped in started the fermentation in a few days. I do not have laboratory conditions at home and can not make my equipment sterile. But I am quite sure that it was my yeast cell that started it.

So we really can conclude that one or a very few yeast cells can start fermentation in a primary or carboy. At least I showed that a few cells can start a fermentation or re-fermentation in a bottle. And that can cause havoc or even exploding bottles.

So make sure you measure the SG and only start bottling when it is below 1000. Or stabilise your sweet wines with sulphite and sorbate.

Luc Volders

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